In many applications it is desirable to produce a spray of fine droplets of a liquid. Such a spray may be used, for example, to cool and cleanse process exhaust gases that are hot and possibly laden with particles and contaminant gases. A two-fluid nozzle atomizes a liquid with a pressurized gas as the liquid is ejected out of the nozzle. The atomized liquid spray from the two-fluid nozzle may be mixed with and thereby cool a process effluent gas. While the nozzle of the present invention is described in connection with the applications of cooling and cleansing process gases, those skilled in the art will appreciate that the nozzle may be used in many applications requiring a fine spray of liquid droplets.
One especially advantageous design of a two-fluid nozzle of the prior art, utilizes a nozzle cap to assist in the production of liquid droplets. An example of the prior art nozzle cap is shown in FIG. 10. FIG. 10 shows a rear perspective view of a prior art nozzle cap 1000, which was used in connection with a nozzle of the type shown in FIG. 1. The nozzle cap 1000 includes an outer frame 1005, a pintle 1010 and support spokes 1015 to support and couple the pintle 1010 to the outer frame 1005. The pintle 1010 comprises an inlet splash plate 1020, a tapered shaft 1025 and an outlet deflector plate (not shown).
The prior art nozzle cap 1000 suffered from several limitations. One limitation of the prior art nozzle cap is its inability to fully atomize some of the liquid. During the atomization of a liquid, the liquid from a liquid feed tube (shown in FIG. 2) strikes the inlet splash plate 1020, forming a thin liquid film. The compressed gas from the high pressure gas source (not shown) creates a turbulent condition near the inlet splash plate. As a result of the turbulent condition at the inlet splash plate, a substantial portion of the liquid from the liquid film flows off of the splash plate 1020, enters the venturi 1030 and exits the nozzle cap 1000 as finely atomized liquid. However, some of the liquid does not enter the venturi 1030 in the turbulent region. Instead, it flows along the support spokes 1015. Most of the liquid flowing along the support spokes 1015 flows off of the spokes near their ends 1040, far from the turbulence near the inlet splash plate and, therefore, does not enter the turbulent region. Consequently, it does not exit the nozzle as fine droplets. Instead, it runs down the interior wall 1035 of the outer frame 1005 and exits the nozzle as coarse droplets. This degrades atomization of the liquid.
The limited atomization is worsened as the liquid film at the inlet splash plate 1020 is improved, ie., reduced in thickness via increased velocity of the liquid exiting the feed tube and the consequent increased radial velocity of liquid flowing radially on the inlet splash plate. An improved liquid film is highly desirable as it results in the production of finer water droplets. However, reducing the thickness of the liquid film at the inlet splash plate 1020 increases the probability of the liquid bypassing primary atomization and exiting the nozzle as coarse droplets. This limits the ability to improve the liquid film.
A second limitation of the prior art nozzle cap 1000 is that the flow of liquid along the spokes and the interior wall 1035 of the outer frame 1005 causes erosion of the support spokes and the interior wall 1035 of the outer frame 1005. As more liquid flows along the support spokes 1015 to the outer frame 1005 of the nozzle cap 1000, without being atomized along the way, there is greater exposure of the support spokes 1015 to the liquid. The flow of liquid along the support spokes 1015, which are generally made of metal, causes them to erode. This erosion tends to be most severe near the end 1040 of the support spokes 1015 closest to the outer frame 1005 of the nozzle cap 1000, where the liquid flows off of the spokes. Eventually, the support spokes 1015 may become so severally eroded that they become detached from the outer frame 1005 of the nozzle cap 1000 and no longer support the pintle 1010, destroying the nozzle cap. Therefore, the liquid flowing along the support spokes 1015 directly contributes to more rapid erosion of the support spokes 1015 and the consequential shorter operational lifetime of the nozzle cap 1000. Similarly, liquid flowing along the interior wall 1035 of the outer frame 1005, which is also usually made of a metal, causes erosion of the interior wall 1035 and degradation of the nozzle cap 1000.